package com.xy.utils;

import java.text.CharacterIterator;
import java.text.StringCharacterIterator;

public class JsonValidatorUtil {
		private CharacterIterator it;
		private char c;
		private int col;
		private static JsonValidatorUtil instance;

		/**
		 * 获取类的实例
		 *
		 * @return 类的实例
		 */
		public static JsonValidatorUtil getInstance() {
				if (instance == null) {
						instance = new JsonValidatorUtil();
				}
				return instance;
		}

		/**
		 * 验证一个字符串是否是合法的JSON串
		 *
		 * @param input 要验证的字符串
		 * @return true-合法 ，false-非法
		 */
		public boolean validate(String input) {
				input = input.trim();
				boolean ret = valid(input);
				return ret;
		}

		private boolean valid(String input) {
				if ("".equals(input)) {
						return false;
				}

				boolean ret = true;
				it = new StringCharacterIterator(input);
				c = it.first();
				col = 1;
				if (!value()) {
						ret = error("value", 1);
				} else {
						skipWhiteSpace();
						if (c != CharacterIterator.DONE) {
								ret = error("end", col);
						}
				}

				return ret;
		}

		private boolean value() {
				return literal("true") || literal("false") || literal("null") || string() || number() || object() || array();
		}

		private boolean literal(String text) {
				CharacterIterator ci = new StringCharacterIterator(text);
				char t = ci.first();
				if (c != t) return false;

				int start = col;
				boolean ret = true;
				for (t = ci.next(); t != CharacterIterator.DONE; t = ci.next()) {
						if (t != nextCharacter()) {
								ret = false;
								break;
						}
				}
				nextCharacter();
				if (!ret) error("literal " + text, start);
				return ret;
		}

		private boolean array() {
				return aggregate('[', ']', false);
		}

		private boolean object() {
				return aggregate('{', '}', true);
		}

		private boolean aggregate(char entryCharacter, char exitCharacter, boolean prefix) {
				if (c != entryCharacter) return false;
				nextCharacter();
				skipWhiteSpace();
				if (c == exitCharacter) {
						nextCharacter();
						return true;
				}

				for (; ; ) {
						if (prefix) {
								int start = col;
								if (!string()) return error("string", start);
								skipWhiteSpace();
								if (c != ':') return error("colon", col);
								nextCharacter();
								skipWhiteSpace();
						}
						if (value()) {
								skipWhiteSpace();
								if (c == ',') {
										nextCharacter();
								} else if (c == exitCharacter) {
										break;
								} else {
										return error("comma or " + exitCharacter, col);
								}
						} else {
								return error("value", col);
						}
						skipWhiteSpace();
				}

				nextCharacter();
				return true;
		}

		private boolean number() {
				if (!Character.isDigit(c) && c != '-') return false;
				int start = col;
				if (c == '-') nextCharacter();
				if (c == '0') {
						nextCharacter();
				} else if (Character.isDigit(c)) {
						while (Character.isDigit(c))
								nextCharacter();
				} else {
						return error("number", start);
				}
				if (c == '.') {
						nextCharacter();
						if (Character.isDigit(c)) {
								while (Character.isDigit(c))
										nextCharacter();
						} else {
								return error("number", start);
						}
				}
				if (c == 'e' || c == 'E') {
						nextCharacter();
						if (c == '+' || c == '-') {
								nextCharacter();
						}
						if (Character.isDigit(c)) {
								while (Character.isDigit(c))
										nextCharacter();
						} else {
								return error("number", start);
						}
				}
				return true;
		}

		private boolean string() {
				if (c != '"') return false;

				int start = col;
				boolean escaped = false;
				for (nextCharacter(); c != CharacterIterator.DONE; nextCharacter()) {
						if (!escaped && c == '\\') {
								escaped = true;
						} else if (escaped) {
								if (!escape()) {
										return false;
								}
								escaped = false;
						} else if (c == '"') {
								nextCharacter();
								return true;
						}
				}
				return error("quoted string", start);
		}

		private boolean escape() {
				int start = col - 1;
				if (" \\\"/bfnrtu".indexOf(c) < 0) {
						return error("escape sequence  \\\",\\\\,\\/,\\b,\\f,\\n,\\r,\\t  or  \\uxxxx ", start);
				}
				if (c == 'u') {
						if (!ishex(nextCharacter()) || !ishex(nextCharacter()) || !ishex(nextCharacter())
							|| !ishex(nextCharacter())) {
								return error("unicode escape sequence  \\uxxxx ", start);
						}
				}
				return true;
		}

		private boolean ishex(char d) {
				return "0123456789abcdefABCDEF".indexOf(c) >= 0;
		}

		private char nextCharacter() {
				c = it.next();
				++col;
				return c;
		}

		private void skipWhiteSpace() {
				while (Character.isWhitespace(c)) {
						nextCharacter();
				}
		}

		private boolean error(String type, int col) {
				//System.out.printf("type: %s, col: %s%s", type, col, System.getProperty("line.separator"));
				return false;
		}
}
